In order to transfer articles from one end of an assembly plant or warehouse, conveyor systems are known which include a plurality of intersecting conveying sections and turntables for changing the orientation of articles being conveyed, or the direction of travel thereof, or both. Turntables which are currently available include those designed for rotating articles on a roller conveyor system and/or rotating a conveying section of a conveyor system. With these known systems, the turntable is usually disposed in a gap between two sections of a non-contiguous conveyor. As a result, several drawbacks exist in that complicated turntable structures are needed for realigning or reorienting an article being conveyed.
In particular, the article is handled more than necessary as it moves across at least three conveying sections. For example, articles or loads are received from one conveying section onto a platform of the turntable. The turntable is rotated through a predetermined angle and then the articles are discharged onto a second section of the conveyor system. The transfer or discharging operation may be done manually or automatically via driven rollers. Likewise, the turntable maybe rotated manually or by a power unit. To assist in the rotating operation, turntables can include means for lowering and raising the articles in relation to the conveying sections. Thus, are several mechanisms are required to rotate an object. This could present problems to an assembly process where stability of an object is extremely important and repositioning of the object being conveyed is necessary so that an operator can do precision work from one side of an assembly line.
U.S. Pat. Nos. 2,897,948 to Cranston, Jr. and 3,100,039 to Oderman et al. disclose a turntable including elevating means and a platform where the piston providing the reciprocal movement of the elevating means is spaced from and parallel to the central axis of the platform supporting the load to be reoriented. Consequently, Cranston and Oderman employ an arrangement including an intermediate lever and a cam which indirectly actuates the raising or lowering operation of the turntable platform. A gear and chain arrangement or plurality of air cylinders provides the rotational movement. Not only are these turntables complicated in structure, the reciprocal and rotational movement thereof may jolt the loads which could be detrimental during the assembly of delicate parts (e.g., top heavy articles or electronic components), or the banding of separate items into a single unit. Further, the platforms of such conventional turntables include a plurality of openings spaced to overlie conveying rollers which complete the gap between conveying sections. When such a platform is lowered, the supported article/load rests on the conveying rollers so that articles can be pushed or conveyed between sections. However, these conventional platforms limit the angular orientation of articles to quarter turns. (i.e., 90.degree., 180.degree., 270.degree., 360.degree.).
A powered turntable assembly having five spaced-apart air jack assemblies which raise and lower a turntable platform within a conveying section is taught by U.S. Pat. No. 4,519,493 to Dyer. This multiple jack assembly provides added stability in the extended position enabling an off-centered load to be raised and rotated. But, this turntable is designed for rotations in increments of 90.degree.. Moreover, a larger number of mechanical connections, as well as pneumatic assemblies, are necessary to complete this structure. Thus, the turntable is expensive to manufacture and to maintain in working condition.
U.S Pat. No. 4,456,116 to Jarman discloses a round platform turntable disposed between two roller conveyor sections and two shortened roller sections. By activating a hydraulic cylinder, a piece of sheet metal positioned on the shortened rollers over the lowered platform turntable is raised above the conveying rollers. As a result, the raised sheet metal can be adjusted and aligned with any desired angle by rotating the platform via a shaft attached to the cylinder. Once the sheet metal is rotated the desired angle, the hydraulic cylinder is activated to lower the sheet metal onto the shortened rollers for continued conveying. However, this system is not concerned with heavy loads or ensuring stability of a conveyed article while being raised or in the extended position.
According to Jarman, the shaft is rotatable about the longitudinal axis of the cylinder. Thus, forces due to a load supported on the turntable platform are transferred through the rotatable shaft and are distributed against the side walls of the shaft and/or hydraulic cylinder. Accordingly, the lifting as well as rotation of a heavy load produces friction, which wears the sealing components of the cylinder requiring replacement or repair. Moreover, the side and load thrusts applied by a load's weight during the rotational and reciprocating motions deteriorate the mechanical connection of the rotating shaft which is initially stable, along with the rubber seals or gaskets disposed on either end of the hydraulic cylinder. Consequently, wobbling is associated with the rotation of such rotatable elevating turntables requiring frequent repair and maintenance.
Accordingly, there is a need in the conveyor art for a turntable of simple construction which provides increased stability of a load carried by a platform in an extended position and during rotation. Moreover, there is a need for a turntable that offers infinite flexibility in precision alignment and orientation of conveyed articles.